1. Field of the Invention
The present invention relates to a method for manufacturing a non-volatile memory cell, and more particularly, to a method for manufacturing a silicon-oxide-nitride-oxide-silicon (hereinafter abbreviated as SONOS) non-volatile memory cell.
2. Description of the Prior Art
Semiconductor memory devices are generally used in computers and electrical products as a means for retaining digital information. Typically, the semiconductor memory devices can be divided into volatile and non-volatile memory devices depending on whether the data stored in the memory devices is completely lost or not in case of power interruption. And the non-volatile memory devices, which can retain data even when the power supply is interrupted, have been widely employed.
In the conventional non-volatile memory technology, a SONOS memory structure is to build a silicon nitride layer sandwiched between two silicon oxide layers for serving as a charge trapping layer while the two silicon oxide layers serve as a charge tunnel layer and a charge block layer respectively. This oxide-nitride-oxide (ONO) multilayered structure is further formed between a semiconductor silicon substrate and a silicon gate, and thus a SONOS memory structure is constructed.
In the electric device including a plurality of SONOS non-volatile memory cells, it is hard to reduce the distance between two adjacent SONOS non-volatile memory cells because some dimension tolerance have to be reserved for the consideration of manufacturing process margin and keeping two adjacent SONOS non-volatile memory cell from overlapping with each other. For instance, the ONO multilayered structure is generally defined by dry etching process and a pad oxide layer has to be used and partially overlapped by the ONO multilayered structure during the dry etching process for protecting the substrate. However, the overlap region between the pad oxide layer and the ONO multilayered structure makes it difficult to reduce the distance between two adjacent SONOS non-volatile memory cells and there will be problems for being applied in more advantage technology node.